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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Lens Types? (Page 1)

 
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Author Topic: Lens Types?
Andrew McCrea
Jedi Master Film Handler

Posts: 645
From: Winnipeg, Manitoba, Canada
Registered: Nov 2000


 - posted 06-24-2004 07:46 PM      Profile for Andrew McCrea   Author's Homepage   Email Andrew McCrea   Send New Private Message       Edit/Delete Post 
Hey Everyone:

I've been looking at SCHNEIDER OPTICS website tonight because I'm looking to learn more about lenses.

My question: Scope is 2.39 and Flat is 1.85. They've bounced around the words Anamorphic and Variable Prime, etc. How do I tell which is which?

Thanks!

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Mike Pennell
Expert Film Handler

Posts: 150
From: Tucson, AZ, USA
Registered: Apr 2003


 - posted 06-24-2004 10:42 PM      Profile for Mike Pennell   Email Mike Pennell   Send New Private Message       Edit/Delete Post 
Anamorphic is scope [beer]

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Christopher Seo
Jedi Master Film Handler

Posts: 530
From: Los Angeles, CA
Registered: Jun 99


 - posted 06-25-2004 02:05 AM      Profile for Christopher Seo   Email Christopher Seo   Send New Private Message       Edit/Delete Post 
The term 'Scope' is derived from 'CinemaScope', which was a specific image/sound format devised by 20th Century Fox utilizing anamorphic lenses. The basic idea behind the CinemaScope image (35mm full-sized frame with 2X anamorphic) survives today. 'Anamorphic' is a generic and more formal term which could be used, I think, to describe any lens that distorts an image by magnifying it by different amounts on the vertical and horizontal axes. Nowadays, 'Scope' and 'anamorphic' are interchangeable as there is only one anamorphic format which one is likely to encounter.

A prime lens has a fixed focal length, whereas a variable prime has a small adjustment range for focal length (much less than a regular zoom lens), so the image size can be tweaked for optimum fit.

The generic term for 'Flat' is 'spherical'. Possibly, 'Flat' refers to movie screens, which were flat before the introduction of CinemaScope (which specified a curved screen). Spherical formats (1.85, 1.66, 1.37) are projected with regular prime lenses (or variable primes). Anamorphic formats are projected either with a combination of a prime lens and anamorphic adapter, or an 'integrated anamorphic' which effectively combines the two into a single tube.

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Ferdinando Innocenti
Film Handler

Posts: 79
From: Genova / Italy
Registered: Jun 2004


 - posted 06-25-2004 03:44 AM      Profile for Ferdinando Innocenti   Email Ferdinando Innocenti   Send New Private Message       Edit/Delete Post 
All right, only one thing: anamorphic is a generic word indicating a distortion in horizontal magnification, as Christopher said. It's used as a synonym for Scope. But in Digital Cinema, and we must be prepared, there are different kinds of aspect ratio in anamorphic lens, such as 1,5:1 or 1,9:1, while in 35mm we have the 2:1 ratio only.

Bye
Nando

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Thomas Hauerslev
Master Film Handler

Posts: 437
From: Copenhagen, Denmark
Registered: Aug 2000


 - posted 06-25-2004 04:44 AM      Profile for Thomas Hauerslev   Author's Homepage   Email Thomas Hauerslev   Send New Private Message       Edit/Delete Post 
Ultra Panavision 70 = 1,25
Cinestage = 1,56

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002


 - posted 06-25-2004 05:49 AM      Profile for Michael Schaffer   Author's Homepage   Email Michael Schaffer   Send New Private Message       Edit/Delete Post 
I always tought "flat" comes from the image being flatter than academy ratio, not from being projected on a flat screen.

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Thomas Hauerslev
Master Film Handler

Posts: 437
From: Copenhagen, Denmark
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 - posted 06-25-2004 07:22 AM      Profile for Thomas Hauerslev   Author's Homepage   Email Thomas Hauerslev   Send New Private Message       Edit/Delete Post 
For me "flat" is an undistorted image ie. non-anamorphic. IMAX is flat for that matter.

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Scott Norwood
Film God

Posts: 7991
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 06-25-2004 07:25 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
1.33, 1.37, 1.66, 1.85, etc. are all "flat"--i.e. not anamorphic. Lenses don't have a concept of aspect ratio, so a 3" lens might be used for 1.85 in one theatre or 1.66 in another. The lens focal length just defines the size of the projected images, with shorter lenses providing larger images, given an equal throw distance.

Someone please correct me if I'm wrong, but my understanding is that a "variable prime" differs from a "zoom" in that the lens does not hold focus when the size adjustment is made. Thus, zoom lenses don't require a focus adjustment when zoomed, while variable prime lenses do.

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David M. Dorn
Film Handler

Posts: 35
From: Hartford, CT USA
Registered: Mar 2004


 - posted 06-25-2004 08:00 AM      Profile for David M. Dorn   Email David M. Dorn   Send New Private Message       Edit/Delete Post 
Variable primes coantain movable elements that allow for small adustments in image size, say +/- 5% of the focal length. A zoom lens usually provides for, at minimum, a doubling of the the lens' prime focal length. Zooms for cinematography may go to 10:1 or more.

The difference is that the variable prime will (or should) show no visable image degradation over its small adjustment range. In the case a projection lens the small adustment range allows a projected image to be trimmed to fit the screen.

Although today's zooms are superb, they still cannot equal top of the line primes; plus they give up some lens speed.

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Frank Angel
Film God

Posts: 5198
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 06-26-2004 06:15 PM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
Michael, I have to go with Christopher on this one -- "flat" comes from the difference that was immediately apparent to projectionists when CinemaScope was first introduced. The screens they had been projecting on up until this time were flat screens. CinemaScope screens were curved to help maintain focus and to concentrate more light back to the seating area. The depth-of-field of the lenses back then wasn't as forgiving as today's computer designed lenses. Also light was now being spread over twice the width of the non-CinemaScope screen and at this juncture getting a bright enough image was a big issue, hence the curvature of the screen. So it was natural for projectionists and industry people to refer to films that were not anamorphic, i.e., not 'Scope, to be "flat" as opposed to curved. The irony that the non-anamorphic films were now also projected on a curved screen seemed to escape them.

Of course today the curved scope screens are gone as they are considerably more expensive to install, so in a majority of theatres, scope is projected on a flat screen making the distinction a distant memory. But "flat" as the generic term to refer to any non-anamorphic, spherically projected image still remains, although it is far from very informative; as Scott has pointed out, it doesn't tell you whether it's flat 1.85, flat 1.75 (used for a while mostly by Disney), flat 1.66, flat 1.37 or flat silent 1.33! Better to just use the aspect ratio width number as the more useful nomenclature.

And as far as Deeeee-Cinema, they have a language all their own. They interchange wide screen to mean letterboxed as well as anamorphic and I have seen DVD releases that claim to be anamorphic when they actually mean letterboxed. And then there is the way they describe aspect ratios. Instead of keeping one parameter (the height) constant, i.e., "x:1," they insist on using different fractions for each, as in 16:9 and 4:3.

Someone once explained in a post that the video way is more accurate, but I can't find that post with a search and quite frankly, I don't see how those numbers are any more informative or more accurate that 2.39:1 or 1.85:1. Seems the cinema ratios directly translate whereas the video method is like comparing apples and oranges.

And it should be mentioned that anamorphic doesn't ALWAYS have to synonomus with a 2.39:1 image, as Thomas points out. There was also an elegant system proposed by Glenn Bergren of ISCO using a "mild" anamorphic and the full film frame height (as is done with CinemaScope) to produce a 1.85:1 screen image without the degredation of resolution and light output that happens with the current cropped spherical wide screen system. That idea has surfaced a number of times over the years because of its many advantages and simple implimentation. If it ever came to pass, who knows what knick-name it would be given to distinguish it from its co-existing counterparts. Perhaps, "Mild-A"....or "Non-cropped Flat"...or "Type A 1.85;" it's anyone's guess.

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Steve Kraus
Film God

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From: Chicago, IL, USA
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 - posted 06-26-2004 07:50 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
...or did "flat" originally mean "not 3D" ?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12207
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-27-2004 09:13 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
A couple points of fact here...curved scope screens are not a thing of the past and curved screens seem to be installed around here quite a bit. Second, curved screens are not considerably more expensive...more like barely more expensive.

As to more accurate numbers in ratios...16:9 is a precise number, 2.39:1 is an approximation to 3 significant digits. Likewise for 1.85:1.

As an example...for "flat" the projection aperture is supposed to be .446" tall by .825" wide....note we are already limiting ourselves to 3 significant figures...Now lets do the math.
.825/.446 = 1.84977578475....etc. Using proper math and limiting to 3 sig. figs...we get 1.85 but that is merely an approximation of the ratio using the data we have. By contrast, 16:9 is a precisely defined ratio using whole numbers and is always accurate. In decimal form...it would be 1.7777777...etc an approximation of its true ratio.

Steve

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Frank Angel
Film God

Posts: 5198
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 06-27-2004 03:18 PM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
So it WAS you, Steve G.! I new someone pointed this out once before. But which numerical format is better to impart aspect ratio information is only a matter of perspective and preference ....you have to like whole numbers. Some of us more poetic types are perfectly happy with rounded-off numbers. Besides, let's face it, any differences three digits after the decimal point are much smaller than any amount of gross overlap that is created by the masking, and consequently this may be important in design mechanics, but irrelevant for purposes of identifying print aspect ratios.

Thing is, 16.9 and 4:3 might be nice and neat for their mathematical wholeness, but they are not any nicer or neater than 2.39 and 1.85 are for their logical unity. It's all in your mindset as to which you prefer. You have to do math (fractionsat that) in your head to visualize what 16.9 and 4:3 actually look like, whereas 2.39:1 and 1.85:1 are much more direct and apparent. Besides, I hate math.

See....techies aren't above talking metaphysics on this board!

And Steve K., yes, you can find tangental references to 3D titles being called "flat" when they were booked for 2D engagements, as in, "DIAL M FOR MURDER only played flat in it's original release," but only in passing and not as a label to distinguish one print format from the other. There was no need to identify whether or not a print was to play 3D or 2D. If you only got one set of reels, it was 2D....the projectionist didn't need too look at the reel bands for a descriptive word to know how to project it.

And I do happily concur that curved screens seem to be having a resurgence here on the East coast as well. There is nothing as pleasing to the eye a picture projected on a slightly curved screen. It imparts a kind of majestic, natural vista to the image -- at least that's what the poet might say; the mathematician would say it has a cord of a certain amount but still love it for its perfection in exactly matching the lens focal points along the curve.

Some of the new builds here have installed curves, yet there are still quite a few new theatres that still retain the flat screen, mostly because they are smaller rooms. I guess if you've got a 15 foot screen, the curve wouldn't be significant enough to impart much of anything.

But you must admit, for decades once the conversion to multiplex was in full swing, curved screens simply disappeared (along with curtains and even movable masking). I would hazard a guess that there are still many more flat screens to curved in NY, probably in a ratio of maybe 7:1....but of course this ratio is only a guestimate and not whole numbers. [Big Grin]

[ 06-28-2004, 12:29 PM: Message edited by: Frank Angel ]

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12207
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-27-2004 09:12 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Frank, in this new DCinema world of the future...what aperture shadow? With lens shifting or having the DCinema projector placed on optical center...what need is there for any spill or an inprecise picture size? As such, 4:3 and 16:9 seem appropriate for video ratios.

As to multiplexes not curving their screens in any era...it didn't necessarily have anything to do with cost and one of the myths I was debunking is that curved screens are anything more than marginally more expensive and often can be proved to be less expensive if done for maximum light reflectance.

There are those that love curved screens and those that hate them. Some of the most high dollar rooms I've been a part of are flat screens because that is what they wanted...cost was not the issue.

Steve

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 06-28-2004 11:09 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
If you use a "gain" screen, it should be properly curved per SMPTE Recommended Practice RP95 to reflect light back to the center of the seating area. Ideally, ray tracing should be used to optimize the curve and tilt of the screen.

Low gain "matte" screens should NOT be curved, as cross-reflections will be more of an issue.

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